Evolutionary approach aims to give a universal key to the problem of optimality in
biology [1]}, [2]}, [3]}. The universal measure of
optimality is Darwinian fitness, that is the reproduction coefficient averaged in a long time
[4]} with some analytic simplifications, when it is possible
[5]}, and with known generalizations for vector distributions
[6]}, [7]}. However, there is no universal rule to measure various traits of
organisms by the changes in the average reproduction coefficient, despite exerted
efforts, development of special methods, and gaining some success
[8]}, [9]}, [10]}, [11]}, [5]}. There may be
additional difficulties because the evolutionary optimality is not necessarily related to
organisms, and the non-trivial question arises: “what is optimal?” Another difficulty is
caused by possible non-stationarity of the optimum: selected organisms change their
environment and become non-optimal on the background of the new ecological situation
[6]}. Nevertheless, the idea of fitness is proved to be very useful. Fitness
functions are defined for different situations as intermediates between the (observable)
traits of the animal and the average reproduction coefficient.
